1. Field of the Invention
This invention relates to helicopter transmissions and rotor hubs generally, and more particularly, to an integrated helicopter transmission and rotor assembly.
2. Description of the Prior Art
Helicopter rotors are generally connected to the helicopter by a drive shaft which is connected to a transmission. All forces generated by the rotor including, lift and various bending moments are carried by the rotor drive shaft. The rotor shaft is in turn connected to the helicopter transmission which, of course, also carries these loads. The transmission reduces the relatively high velocity low torque input from the helicopters engine to a low RPM high torque output to drive the rotor through the rotor shaft.
Since both certain portions of the transmission and the rotor shaft carry all of the loads generated by the rotor, these components are relatively heavy.
The transmission is generally located in the top portion of the helicopter fuselage. The rotor shaft and rotor are, of course, located above the transmission. The rotor controls which cause rotation of the rotor blades about their pitch axis are also generally located between the rotor and the fuselage. The swashplate is generally located below the blades and includes rotating and non-rotating components. Pitch links connect the blades to the rotating portion of the swashplate. Push-pull rods, which are connected to the non-rotating portion of the swashplate, are connected to pitch actuators which are connected to the fuselage.
A helicopter rotor is, of course, generally located above the aircraft fuselage. For any particular helicopter design there is an optimum height the rotor should be positioned above the aircraft. If the rotor is above that optimum height a weight and aerodynamic penalty may be incurred. The excess weight results from the added structure while the aerodynamic penalty is primarily in the form of excess drag.
If the rotor height is below the optimum height other problems arise, mainly from aerodynamic interaction between the body of the aircraft and the rotor. Excess vibration, noise and various aerodynamic effect are the types of problems which may arise in this instance.
In general the helicopter designer's problem is to lower the rotor towards the optimum height. This primarily results from the current configurations of transmissions and rotors, coupled with the requirement that the transmission be located in the top of the aircraft fuselage in order to provide adequate internal cabin space. In some cases this latter requirement forces the transmission to protrude above the fuselage. Additionally, the rotor is forced upwards in order to make room for the rotor control system, including the swashplate and pitch actuators.
The added increment of height required to accommodate the pitch actuators and swashplate extends the drive shaft with an attendant increase of weight.
These problems are generally recognized and well known in the helicopter art. The invention disclosed in U.S. Pat. No. 3,486,832 issued Dec. 30, 1969 to Stone lowers a helicopter rotor head by integrating a helicopter transmission with a rotor drive shaft. Stone also integrates the transmission and swashplate.
The invention disclosed in U.S. Pat. No. 3,080,002 issued Mar. 5, 1963 to DuPont lowers the height of a helicopter rotor by placing the swashplate above the rotor head.